MPLS entropy label
To perform load balancing in an MPLS environment, deep packet inspection (DPI) was necessary to determine how traffic is to be load balanced. This was necessary at each MPLS hop, which introduced much overhead.
With the introduction of the MPLS LDP entropy label, DPI is performed only once at the ingress interface where MPLS is encapsulated. From this inspection, an entropy label is generated. Thus, at the transit node there is no need to perform DPI again. Load balancing is then determined base on the entropy label.
When DPI is performed at the ingress LER, appropriate keys are extracted from a given packet and are input into the load balancing function. The results are placed within the entropy label which exists within the MPLS label stack. Transit MPLS routers are then responsible for using that information to perform load balancing.